For the purpose of power saving, CO2 reduction, etc., there is a demand for further enhancing the functionality of electromagnetic motors, whereby enhancements in performance, represented by reduction in size and weight and increases in efficiency, torque and output, etc., are now being made significantly. When electromagnetic motors are roughly classified based on magnetic flux direction, they can be grouped into (1) radial flux motors, (2) axial flux motors and (3) transversal flux motors. Among these types, the radial flux motors are excellent especially in cost performance, and have been widely used so far for various products as typical machinery elements for versatile actuators. The axial flux motors have such a structural feature that they can be adapted to complex three-dimensional magnetic paths, but conventionally widely used laminated steel plates are hard to use for them. The axial flux motors are used as, in particular, medium/large-size thin motors of a large bore diameter.
Further, the transversal flux motors are each characterized by a structure in which base units are arranged along the rotation axis of the motor in two or more stages at predetermined relative phase angles with respect to the rotation axis, each base unit comprising a rotor with permanent magnets, and an armature (forming a division-type toroidal core structure) provided with an annular coil provided around the rotation axis of the rotor, and with a plurality of substantially U-shaped stator cores (hereinafter, “U-shaped stator cores”) circumferentially provided around the annular coil. This structure can relatively easily produce a highly efficient magnetic field, utilizing high torque resulting from the multi-stage structure and the division-type toroidal core structure. Namely, in general, the transversal flux motors can be easily made to have multi-polarity since it is sufficient if a plurality of U-shaped stator cores are arranged around the rotation axis, compared to a radial flux motor or an axial flux motor that needs a dead space for, for example, assembling and inserting a stator core with a plurality of slots arranged around the rotation axis, and a coil wound on the slot portions. Furthermore, since in the transversal flux motors, the armature comprising the annular coil and the U-shaped stator cores (division-type toroidal cores) is of a structure in which the magnetic flux generated by the coil does not easily leak out, the magnetic field production efficiency by the coil is high. Therefore, the transversal flux motors can be made more compact than the radial flux motors or axial flux motors.
JP-B No. 408059, for example, discloses a conventional motor.
However, in the disclosed conventional transversal flux motor, U-shaped stator cores are employed, and the two magnetic pole portions of each U-shaped stator core are arranged along the rotation axis. At least two permanent magnets for generating torque are provided at the appropriate portions of the rotor corresponding to the armature with the U-shaped stator cores, with the result that the axial length of the rotor becomes long and hence the base unit cannot be made compact.
Moreover, in the case of the multi-stage structure, it is necessary to provide, in view of preventing magnetic interference, a plurality of base units with a predetermined magnetic space between each pair of adjacent base units. This further increases the size of the motor.
In addition, the long axis of the rotor as a rotary machine is not always satisfactory in the aspect of performance, since reduction of high-speed response due to an increase in the inertia of the rotor, and degradation of stability of rotation due to the vibration characteristic of the rotor, will be involved. As a result, the motor size is inevitably increased and the motor becomes more expensive.